// Ceres Solver - A fast non-linear least squares minimizer
// Copyright 2026 Google Inc. All rights reserved.
// http://ceres-solver.org/
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// Author: sergiu.deitsch@gmail.com (Sergiu Deitsch)

#ifndef CERES_PUBLIC_INTERNAL_COMPENSATED_MATH_H_
#define CERES_PUBLIC_INTERNAL_COMPENSATED_MATH_H_

#include <type_traits>
#include <utility>

namespace ceres::internal {

// Similar to Fast2Sum, but without requiring ordering or a specific radix.
template <typename T>
constexpr auto TwoSum(T a, T b)
    -> std::enable_if_t<std::is_floating_point_v<T>, std::pair<T, T>> {
  const T s = a + b;
  const T a_prime = s - b;
  const T b_prime = s - a_prime;
  const T delta_a = a - a_prime;
  const T delta_b = b - b_prime;
  const T t = delta_a + delta_b;
  return std::make_pair(s, t);
}

}  // namespace ceres::internal

#endif  // CERES_PUBLIC_INTERNAL_COMPENSATED_MATH_H_